Why Do Ice Rinks Stay Frozen?

Hockey. Figure skating. Speed skating. Curling. What do these sports have in common?

You guessed it -- they all take place on ice! It’s not surprising that they are also all popular sports in Canada. Have you ever wondered how ice for sports is created?

Did you know?

Researchers think ice skating first originated in Finland around 5 000 years ago! Early skates were made of bone. They were likely used as a way to cross frozen ponds and lakes. 

Why does ice form on the surface of water?

As you know, the three most common states of matter are solids, liquids, and gases. In solids, the tiny molecules that make up matter (atoms) are tightly packed together. On the other hand, atoms of liquids and gases are less tightly packed together. That’s why these substances can flow around or be poured. Most liquids become more dense when they change from a liquid to a solid. This is why denser materials typically sink when placed in a less-dense material. But this is not the case when it comes to ice! 

Liquid water is most dense at about four degrees Celsius. It becomes less dense when it becomes a frozen solid. This is why ice cubes float when you put them in your drink! But why is water different from most other substances? 

Did you know?

One effect of hydrogen bonding in liquid water is high surface tension. It’s what allows animals like water striders to walk on the surface of water.

What makes water act this way?

A water molecule is made up of two hydrogen atoms and one oxygen atom (H₂O). Hydrogen and oxygen are polar molecules, so they form polar covalent bonds. The electrons in water molecules spend more time closer to the nucleus of the oxygen atom than the hydrogen atoms. This is due to oxygen’s high electronegativity. Water molecules are known as polar. This is because of the unequal sharing of electrons, and its bent shape.

Water is considered a neutral molecule overall. But because of its polarity, hydrogen has a slight positive charge and oxygen has a slightly negative charge. This means that it’s highly attractive to other water molecules. This attractiveness gives rise to hydrogen bonds that form between water molecules. Or in other words, the oxygen atom of one water molecule will be attracted to the hydrogen atoms of other water molecules.  

When water is in its liquid state, the molecules are in constant motion. They stay relatively close together. But when water freezes and turns to its solid state (ice), hydrogen bonding forces the molecules into a crystal lattice of hexagons. This crystal lattice looks like the pattern on a soccer ball. This process makes it harder for the molecules to move. It pushes them slightly further away from each other. This is what makes ice less dense than water.

Did you know?

Glycol is an alcohol with two hydroxyl groups (OH). It stays liquid even at temperatures below zero degrees Celsius. It is often used in the pipes beneath ice rinks. 

How can we keep ice rinks frozen?

Natural ice rinks, like frozen lakes, depend on cold weather. But some artificial rinks have special cooling technologies that allow you to skate on them even when the temperature is above zero degrees Celsius. 

Some of these specialized technologies rely on gases to provide heating or cooling properties. But before you can understand how this process works, you’ll need to understand the Gas Laws. These laws are comprised of Boyle’s Law, Charles’ Law, and Avogadro's Law. 

Boyle’s Law states that the volume of gas increases when the pressure decreases. Charles’ Law states that the volume of gas increases as the temperature increases. Avogadro’s Law states that the volume of gas increases as the amount of gas increases. 

The technologies that put ice on artificial rinks were designed with these laws in mind.

One example is the Michigan Tech Ice Rink. There, electricity powers a compressor that packs the molecules of a chemical refrigerant  (such as ammonia [NH3] gas or more recently, carbon dioxide gas [CO2], which is safer if leaks happen) closer together until they become liquid. This releases a lot of unwanted heat energy. This heat is either vented away or used in some other process.

The compressed liquid is then allowed to expand back into a gas. To expand, it needs to take in the same amount of energy as it gave off when it was compressed. It takes in this energy in the form of heat. The gas absorbs heat from its surroundings, making everything near it very cold.

The chilly gas is then used to cool a liquid called brine. Brine is a very salty water solution. It gets pumped through pipes underneath the ice rink. And voilà, cold ice in mild weather - or even indoors!